Our long-term goal is to understand the pathogenesis of bacterial otitis media and to develop a multivalent vaccine that reduces the incidence of otitis media caused by all major bacterial pathogens in children. Lipooligosaccharide (LOS), a major bacterial surface component of Moraxella catarrhalis, is a possible virulence factor in the pathogenesis of human infections caused by the organism. In the passing year, we have identified a gene (lpxA) in M. catarrhalis, which is responsible for the first step of biosynthesis of endotoxin, enabling the creation of a highly immunogenic, endotoxin-free knockout mutant without endotoxin with promise as a vaccine candidate or vaccine vehicle. [unreadable] [unreadable] Besides, in an effort to improve current vaccine candidates for another pathogenic bacterium, nontypeable Haemophilus influenzae (NTHi), which also causes otitis media in children, we used outer membrane protein P6 as a new carrier for NTHi LOS conjugate vaccines. Our studies in experimental animals indicate that P6 could serve as an effective carrier for conjugate vaccines and have a potential to generate better immune responses in animals. [unreadable] [unreadable] To further explore a current vaccine candidate for NTHi, we investigated the kinetics of humoral immunity and its related cellular immune responses to intranasal immunization with an LOS based conjugate vaccine against the pathogenic NTHi bacterium in mice. Our findings may provide useful information regarding to effective mucosal vaccines against NTHi infections in vivo.